Geochemical, textural and micromorphological properties of Angolan agroecosystem soils in relation to region, landscape position and land management

Abstract

Angola is a country rich in natural resources, containing enormous water resources and a vast area of land yet to be developed. It has a mostly young population, where subsistence family farming supports 90% of the rural population. The country was once an agricultural power in the colonial era, but today its production levels are low, and while soils are potentially suitable for agriculture the status of nutrient elements and related management practices are poorly understood. The concepts of soil improvement are related to the sustainability approaches needed for new agricultural developments in Angola. This project studies Angolan soils with the aim of contributing to a better understanding of the status of nutrient elements and the factors that determine their levels. The objectives of the thesis are to: a) Determine nutrient element status in the agricultural regions of Luanda and Huambo in Angola, the areas of greatest agricultural expansion in the country. Soil sampling for this purpose was based on catena-based soil transects and field profile horizon characteristics of the region’s Ferralsols soils. Soils from two provinces were subject to chemical, physical and micromorphological analysis with the aim of understanding aspects related to characteristics mentioned above and their genesis. Analyses was based on Coulter Counter (textural), ICP-MS (Inductively Coupled Plasma Mass Spectrometry), thin section micromorphology and associated SEM-EDX (Scanning Electron Microscopy-Energy dispersive X-ray spectroscopy) analyses. Levels and locations of nitrogen (N), phosphorus (P), potassium (K) and pH values. b) explain the nutrient element levels in terms of the relative contributions of micromorphological properties, soil texture and cultural amendment of soils. Weathering assessments were undertaken through thin section micromorphology, highlighting both physical and chemical weathering fronts on mineral grains; texture was assessed by using particle size analysis in combination with analysis related pedogenic- features in thin section; and the nature of soil amendments undertaken by subsistence farmers has been assessed through a series of farmer interviews. The findings of this study show that the contents of the macronutrients are higher than the micronutrients. This study shows that the soils have a silty clay loam and silt loam textural classes, with exception of the Ramiro region which, presented a sand texture. Moreover, the textural classes were observed to be related to nitrogen (N) status in relation to profile and depth. The micromorphological and microchemical analysis showed the high degree of weathering of these soils and kaolinite and quartz as the main mineral present, while the highest level of K and P were observed in the fine material. Integration of soil nutrient element status and the explanatory factors has a fundamental significance for Angola and the Southern Africa region with the Southern African Development Community (SADC) now expressing an interest in applying the findings into developing new policies to support subsistence farmers.